It is a known fact that salts of pyruvic acid (pyruvates) have valuable physiological, therapeutic and dietetic properties. Pyruvates, especially calcium pyruvates, are used to enhance long-term performance and strength in the field of sport, to reduce weight and body-fat in the field of health care, where it is also used as a protective substance for body cells and tissues (in particular for cardiovascular, hepatic, nephrotic, peritoneal and neuronal tissue), as a substance which inhibits the formation of free radicals and as a substance which scavenges free radicals in body cells and tissues (including synovial tissue). Pyruvates are also used as food supplements, wound-healing agents and for the treatment of kidney diseases (acute kidney failure and nephrolithiasis).
Of the pyruvate salts, sodium and potassium pyruvates, however, are little suited for therapeutic applications or as food supplements on account of their sodium- and potassium-ion content. In contrast to alkali-metal ions, calcium ions do not result in any physiological side effects, which means that calcium pyruvates can safely be used for therapeutic purposes and as a food supplement.
There are only two methods which have been described so far in the prior art for producing calcium pyruvates. According to the article published by K. Jowanowitsch in "Monatshefte" Nr. 6, pp. 467-476 (1885), tartaric acid in glycerin is dehydrated or decarboxylated to a glycidyl pyruvate, which subsequently reacts with lime in aqueous solution to form calcium pyruvate. As was established by proceeding according to the examples contained in this publication, this process does not result in the formation of calcium pyruvates but of polymeric pyruvic acid derivatives.
According to French patent no. 1 465 432, calcium pyruvate is obtained by neutralizing pyruvic acid with calcium carbonate, hydroxide or oxide in water. The disadvantage of this method is the fact that only impure or unstable calcium pyruvates are obtained, which contain more than 2.5 mol water of crystallization and occur in the form of 2,2-dihydroxypropionate ions. These reaction products as a rule contain little calcium pyruvate and comparatively large quantities of by-products, since the pyruvic acid or pyruvate ion reacts by way of aldol addition or aldol condensation to form acyclic or cyclic dimers and polymers of pyruvic acid. With respect to acyclic compounds, particular mention is made here of para-pyruvic acid (4-hydroxy-4-methyl-2-oxoglutaric acid) and its salts, and of the higher aldol-addition products. Oxalic acid and methyl succinic acid may also form as by-products.
By way of lactonization, ketalization, and other reactions, the acyclic pyruvic-acid polymers can, in turn, form cyclic compounds such as 2-hydroxy-2-methyl-4-oxoglutaric acid-5-lactone and derivatives of trimesic, isophthalic and pyran tricarboxylic acids. These by-products can form in a similar way when calcium pyruvates containing more than 2.5 mol water of crystallization are stored.
The calcium pyruvates known from the prior art are thus not suitable for therapeutic uses (free-radical scavenger, cellular protection, obesity etc.) or as a food supplement, because during production and storage of these pyruvates by-products and decomposition products of pyruvic acid and its salts are formed which may be physiologically incompatible or even toxic.